Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
  • G01N21/3586—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation by Terahertz time domain spectroscopy [THz-TDS]
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
  • G01B11/00—Measuring arrangements characterised by the use of optical techniques
  • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
  • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
  • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
  • G01N21/35—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light
  • G01N21/3581—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using infrared light using far infrared light; using Terahertz radiation
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/41—Refractivity; Phase-affecting properties, e.g. optical path length
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/47—Scattering, i.e. diffuse reflection
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
  • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
  • G01N21/47—Scattering, i.e. diffuse reflection
  • G01N21/4795—Scattering, i.e. diffuse reflection spatially resolved investigating of object in scattering medium
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/061—Sources
  • G01N2201/06113—Coherent sources; lasers
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/063—Illuminating optical parts
  • G01N2201/0638—Refractive parts
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N2201/00—Features of devices classified in G01N21/00
  • G01N2201/06—Illumination; Optics
  • G01N2201/069—Supply of sources
  • G01N2201/0696—Pulsed
  • G01N2201/0697—Pulsed lasers

Definitions

• he present invention relates to a measurement
• the present invention also relates a tomography apparatus and method.
• Terahertz waves typically are electromagnetic waves
• Such frequency bands include many characteristic absorption bands derived from structures or states of various substances including biomolecules . Using such characteristics, inspection techniques of non-destructive analysis or
• reflection terahertz waves from a refractive index interface in an object to be measured are applied to a tomography apparatus configured to visualize an inside of the object to be measured.
• a tomography apparatus configured to visualize an inside of the object to be measured.
• Such an apparatus is expected to visualize an inner structure at a depth of several hundreds of ⁇ to several tens of mm using a characteristic of transmission of terahertz waves.
• spectroscopy apparatus performs sampling measurement using ultrashort pulsed lights (also herein referred to as excitation lights) having a femtosecond pulse width. Sampling of the terahertz waves is achieved by
• an optical path length difference between excitation lights reaching a generation unit configured to generate the terahertz waves and a detection unit configured to detect the terahertz waves is adjusted
• a stage also herein referred to as a delay optical unit
• a photoconductive element having an antenna electrode pattern with a minute gap provided on a semiconductor thin film is used as the generation unit or the detection unit.
• physical properties of an object to be measured are obtained using the principle of a THz-TDS apparatus.
• the physical properties of the object to be measured mainly include a refractive index and a shape (thickness) of the object to be measured. These physical properties are often calculated using terahertz wave pulses, from a time difference between reflection pulses from a refractive index interface of the object to be measured (see PTL 1).
• An interval between the reflection pulses corresponds to an optical length of propagation of terahertz waves.
• the optical length of the terahertz waves is expressed in the form of n(ave)*t by
• the average refractive index refers to a typical refractive index of the object to be measured.
• the average refractive index refers to an average value of
• the average refractive index refers a refractive index at frequency (wavelength) having highest intensity in a frequency spectrum of the object to be measured. It is difficult to calculate the thickness t and the average refractive index n(ave) of the object to be measured from a measurement result of the terahertz waves because there is only one
• PTL 1 calculates a refractive index of an object to be measured by another unit.
• a refractive index of an object to be measured by another unit As such, to separate the thickness t and the average refractive index n(ave) from the measurement result, either of them needs to be obtained using another measurement unit.
• properties of the object to be measured are desirably specified to some degree before measurement. However, such an act may limit an
• thickness t and an average refractive index n(ave) are simultaneously calculated from, an amount of movement of a focus in a collecting position of the confocal optical system in a depth direction of an object to be measured, and an amount of change of an optical path length difference of an interference system required for obtaining a maximum interference signal for each focus.
• the thickness t and the average refractive index n(ave) of the object to be measured are calculated from a ratio of the amount of change of the optical path length difference to the amount of movement of the focus (see PTL 2) .
• TL 2 Japanese Patent No. 3602925
• a position of a refractive index interface connecting focuses needs to be accurately calculated. Since a wavelength used in the OCT apparatus is several ⁇ or less, a depth of focus in the confocal optical system becomes several tens of ⁇ . Thus, for an object to be measured having a thickness of several hundreds of ⁇ to several tens of mm, the depth of focus is
• the focus of the optical system can be recognized as a point. This makes clear a boundary of the refractive index
• the confocal optical system includes a region where the beam is in a process of being collected (also herein referred to as a collecting process region) and the collimated region described above, and the system is often used on the assumption that the object to be measured is
• the collimated region is a region with a reduced function of the confocal optical system.
• the focus of the optical system is defined as a certain region rather than a point. If the object to be measured having substantially the same size as the collimated region is measured in the confocal optical system, an influence of the amount of movement of the focus is relatively increased. This makes unclear the boundary of the refractive index interface of the object to be measured, and it reduces measurement accuracy of the thickness t and the average refractive index n(ave) of the object to be measured. This phenomenon occurs when the object to be measured of substantially the same size as the collimated region in the confocal optical system is measured, with any wavelengths, not limited to the terahertz waves.
• a measurement apparatus of the present invention configured to apply electromagnetic wave pulses to an object to be measured to obtain a physical property of the object to be measured
• a detection unit configured to detect the electromagnetic wave pulses from the object to be measured
• a delay optical unit configured to adjust an optical path length difference between the
• electromagnetic wave pulses reaching the detection unit and an excitation light reaching the detection unit for detecting the electromagnetic wave pulses reaching the detection unit and an excitation light reaching the detection unit for detecting the electromagnetic wave pulses; a shaping unit configured to collect the electromagnetic wave pulses on the object to be measured; a waveform
• obtaining unit configured to refer to an output from the detection unit and an amount of adjustment of the optical path length difference by the delay optical unit to construct a time waveform of the
• a collecting position adjusting unit configured to adjust a relative position between the object to be measured and a collecting position
• a measurement position information obtaining unit configured to obtain positions of the reflection portions of the object to be measured as an amount of adjustment by the collecting position adjusting unit, and an optical path length difference by the delay optical unit required for detecting a part of the time waveform of the pulses from the reflection portions at the amount of adjustment
• a physical property obtaining unit configured to obtain an amount of adjustment Zi by the collecting position adjusting unit when the collecting position of the electromagnetic wave pulses matches the first reflection portion of the object to be measured, an optical path length
• the positions of the reflection portions can be
• terahertz wave pulses are used as the electromagnetic wave pulses, using transmission of the terahertz wave pulses allows visualization of an inner structure at a depth of several hundreds of ym to several tens of mm, and specification of the physical property.
• FIG. 1 is a schematic configuration diagram of an
• FIG. 2 is a schematic configuration diagram of an apparatus described in Embodiment 2.
• FIGS. 3A and 3B are schematic configuration diagrams of an apparatus described in Embodiment 3.
• FIG. 4 illustrates an operation of the apparatus of Embodiment 1.
• FIG. 5 illustrates an operation of the apparatus of Embodiment 2.
• FIGS. 6A and 6B illustrate a beam shape and a
• FIGS. 7A, 7B and 7C illustrate an operation of a measurement position information obtaining unit.
• FIGS. 8A, 8B and 8C illustrate a method of increasing accuracy of the measurement position information obtaining unit.
• FIGS. 9A, 9B and 9C illustrate a method of increasing accuracy of the measurement position information obtaining unit.
• FIGS. 10A, 10B and IOC illustrate an object to be measured used in Example 1.
• FIGS. 11A and 11B illustrate an operation of a
• FIGS. 12A and 12B illustrate an operation of the measurement position information obtaining unit in Example 1.
• FIG. 13 is a schematic configuration diagram of an apparatus described in Embodiment 4.
• FIG. 14 illustrates an operation of the apparatus of Embodiment 4.
• FIGS. 15A and 15B are schematic diagrams of skin.
• FIGS. 16A and 16B are schematic diagrams of an object to be measured and a tomographic image thereof.
• FIG. 17 illustrates processing accuracy of the
• a position of a reflection portion (such as a refractive index interface) of an object to be measured is calculated from a change of a time waveform that follows a change of a collecting position of electromagnetic wave pulses with respect to the object to be measured.
• the collecting position is typically a collimated region described later in a portion where the electromagnetic wave pulses are collected.
• FIG. 1 is a schematic configuration diagram of a physical property measurement apparatus of this embodiment.
• the physical property measurement apparatus of this embodiment includes at least: a
• generation/detection unit 101 configured to generate and detect electromagnetic wave pulses
• a shaping unit 102 configured to shape and collect the
• generation/detection unit 101 to generate and detect the electromagnetic wave pulses by; a delay optical unit 104 configured to adjust an optical path length difference between the electromagnetic wave pulses and the excitation light at a time when the
• a waveform obtaining unit 105 configured to obtain a time waveform of
• electromagnetic wave pulses are collected with respect to the object to be measured; a measurement position information obtaining unit 107 configured to refer to outputs from the waveform obtaining unit 105 and the collecting position adjusting unit 106, and calculate positions of the reflection portions of the object to be measured; and a physical property obtaining unit 108 configured to refer to outputs from the waveform
• terahertz waves are used as the electromagnetic wave pulses for description, but a wavelength of the electromagnetic wave pulses in the present invention is not limited to a wavelength of a terahertz wave region.
• he generation/detection unit 101 generates and detects terahertz wave pulses.
• the generation/detection unit 101 converts a change of electric field strength of the terahertz waves into a change of a current output from an element for detection.
• a current corresponding to electric field strength of terahertz waves is detected by a change of photoconductivity in application of an excitation light.
• an element also herein referred to as a photoconductive element having an antenna pattern formed of a metal electrode on a semiconductor film is applicable. Otherwise, an electric field can be
• a magneto-optic effect can be detected using a magneto-optic effect herein.
• a polarization splitter and an electro-optic crystal may be used.
• a magneto- optic effect is used to detect a magnetic field, a polarization splitter and a magneto-optic crystal may be used.
• portion configured to generate the terahertz waves may be shared with or separated from a portion for
• generation/detection unit 101 can generate and detect the terahertz waves with the same element configuration.
• an irradiation of an excitation light to a surface of a semiconductor or a nonlinear crystal may be applied to generate terahertz waves using an
• a photoconductive element may be used to apply an electric field to an electrode of the photoconductive element when applying an excitation light to generate terahertz waves.
• An electro-optic effect of a nonlinear crystal may be used to generate terahertz waves by polarization generated by
• a PIN diode structure may be applied.
• interband transition of a carrier in a semiconductor quantum well structure may be used.
• An example in which a photoconductive element is used as the generation/detection unit 101 is mainly
• the shaping unit 102 adjusts a beam shape of terahertz wave pulses.
• the shaping unit 102 is constituted by a casing with a window enclosing two lenses and the generation/detection unit 101.
• the shaping unit 102 collects the terahertz wave pulses using the two lenses 109 and 110.
• the shaping unit 102 may include an actuator 111 configured to move the lens on a window side in a propagation direction of the terahertz wave pulses. By adjusting a position of the lens 110 on the window side, a collecting position can be adjusted.
• the shaping unit 102 When the shaping unit 102 encloses the generation/detection unit 101, the shaping unit 102 itself may have a mechanism moving in the propagation direction of the terahertz wave pulses so that a position where the terahertz wave pulses are collected is adjusted in the propagation direction of the terahertz wave pulses. Since the shaping unit 102 may only required having a function of collecting the terahertz wave pulses, it may include a mirror in place of the lens. As shown in FIGS.
• the beam shape of the terahertz wave pulses collected by the shaping unit 102 can wave-optically be classified roughly into a region in a process of the terahertz wave pulses being collected (region A, also referred to as a light collecting process region) and a region where the terahertz wave pulses propagate in a
• region B also referred to as a collimated region
• the light source 103 supplies an excitation light to a photoconductive element that constitutes the
• the light source 103 outputs an ultrashort pulse laser.
• the pulse laser output from the light source 103 has a pulse width of several tens of femtoseconds.
• generation/detection unit 101 operates by exciting a carrier on a semiconductor thin film by application of an excitation light. As shown in FIG. 1, the
• excitation light output from the light source 103 is split into optical paths L x and L 2 by a beam splitter 112.
• An excitation light passing through the. optical path Li is applied to the generation/detection unit 101 and used for generation.
• An excitation light passing through the optical path L 2 is applied to the
• a delay optical unit 104 described later and used for detection.
• wavelength of the excitation light emitted from the light source 103 changes depending on absorption
• the generation unit and the detection unit of the terahertz waves are configured to be a common element, they may be
• a wavelength conversion element may be provided in a middle of the optical path Li or L 2 .
• a wavelength, a pulse width of the light source 103, or a repetition frequency of the laser are selected
• the common photoconductive element is used for generating and detecting the terahertz waves, and thus the excitation lights passing through the optical paths Li and L 2 are again combined into the same optical path by the beam splitter immediately before the
• he delay optical unit 104 that is a delay portion adjusts optical path lengths of the excitation lights, and adjusts an optical path length difference between the excitation lights Li and L 2 reaching the
• the optical path length difference between the excitation lights Li and L 2 incident on the generation/detection unit 101 is successively changed by a predetermined amount to perform sampling
• the delay optical unit 104 may directly adjust the optical path length of the excitation light, or adjust an effective optical path length.
• a folded optical system configured to fold the excitation light and a movable portion configured to move the optical system in a folded direction may be used.
• a rotating system may be used as the movable portion so that the folded optical system moves in a rotational direction of the movable portion.
• the light source 103 two laser sources configured to output the excitation lights Li and L 2 may be used to change the repetition frequency of each laser. In this case, a time difference between the two excitation lights reaching the generation/detection unit 101 relatively changes, and thus the time difference can be converted into an optical path length difference.
• the configuration of the delay optical unit 104 is not limited to this, and any method may be used for
• FIG. 1 illustrates an example of using the folded optical system.
• he waveform obtaining unit 105 refers to an output from the generation/detection unit 101 and constructs a time waveform of the terahertz waves.
• the terahertz waves typically have a pulse waveform of picosecond or less, and it is difficult to obtain the time waveform in an actual time.
• sampling measurement is performed with a pulsed light having a smaller pulse width than a pulse width of the terahertz wave.
• a pulsed light used for sampling is the above described excitation light.
• the excitation light is a pulsed light having a femtosecond pulse width.
• the sampling measurement of the terahertz waves is performed by adjusting an optical path length
• the optical path length difference is adjusted by the above described delay optical unit 104.
• obtaining unit 105 monitors an amount of adjustment of the optical path length difference by the delay optical unit 104 for the terahertz waves reaching the
• generation/detection unit 101 plots an output from the generation/detection unit 101 depending on the amount of adjustment to construct a time waveform of the terahertz waves.
• the collecting position adjusting unit 106 wave- optically refers to a portion which moves the
• the collecting position adjusting unit 106 moves the collecting position of the terahertz wave pulses from a position Pi on the first reflection portion 114 to a position P2 on the second reflection portion 115.
• the positions Pi and P2 are shown by points, but they actually are certain regions.
• the collecting position adjusting unit 106 controls the actuator 111 provided in the shaping unit 102 to move the lens 110 on the side of the object to be measured substantially along the optical axis of the terahertz waves, and thus it adjusts the collecting position of the terahertz wave pulses.
• the collecting position adjusting unit 106 moves a position of the shaping unit 102 substantially along the optical axis of the
• the object to be measured is placed on the actuator 116, and the
• actuator 116 moves the position of the object to be measured substantially along the optical axis of the terahertz waves to relatively adjust the collecting position of the terahertz wave pulses.
• the measurement position information obtaining unit 107 obtains a position of the first reflection portion 114 of the object to be measured from a change of the time waveform of the terahertz wave pulses with a change of the collecting position of the terahertz wave pulses. More specifically, the measurement position information obtaining unit 107 obtains a position where the
• the collecting position P x of the terahertz wave pulses focused by the shaping unit 102 matches the first reflection portion 114 of the object to be measured.
• the collecting position of the terahertz wave pulses is adjusted by the collecting position adjusting unit 106.
• Concerning the time waveform of the terahertz wave pulses the time waveform constructed by the waveform obtaining unit 105 is referred to.
• shapes of a first pulse from the first reflection portion 114 of the object to be measured and a second pulse from the second reflection portion 115 are referred to.
• the first reflection portion 114 is located. in a position closer to the
• the measurement position information obtaining unit 107 is an amount of adjustment by the collecting position adjusting unit 106, and an amount of adjustment by the delay optical unit 104 required for detecting a pulse waveform (a part of the time waveform corresponding to the
• FIG. 6A illustrates a beam shape of the terahertz wave pulses in the
• FIG. 6B illustrates time waveforms of the first pulse and the second pulse of the terahertz wave pulses obtained from the reflection portions.
• the region in a process of the terahertz wave pulses being collected is referred to as the light collecting process region (region A)
• the region where the terahertz wave pulses propagate in a collimated shape is referred to as the collimated region (region B) .
• the collimated region wave-optically corresponds to a depth of focus.
• the collecting position by the shaping unit 102 is included in the collimated region.
• refractive index is n(ave)
• an optical length of the terahertz waves propagating through the object to be measured approximates to txn.
• an amount of movement of the collimated region in the object to be measured approximates to t/n(ave) in view of an angle of refraction of the terahertz waves with respect to the object to be measured.
• the amount of movement of the collimated region is equivalent to the amount of movement of the collecting position herein for
• the physical property obtaining unit 108 described later calculates the optical length and the amount of movement of the collimated region from the optical path length difference by the delay optical unit 104 and the amount of adjustment by the collecting position adjusting unit 106, and uniquely calculates the thickness t and the average refractive index n(ave) of the object to be measured.
• a propagation length of the terahertz waves reaching the generation/detection unit 101 is a value including the moving distance of the reflection portion and an angle component with scaling up and down of a beam diameter.
• the optical moving distance of the reflection portion with the movement of the reflection portion is longer than the optical moving distance in the collimated region (region B) .
• the optical moving distance can be converted into a propagation time of the terahertz wave pulses. Based on the above described phenomenon, the physical
• the property obtaining apparatus with the terahertz wave pulses detects the pulses from the first reflection portion 114 and the second reflection portion 115 of the object to be measured, in which a time interval between the first pulse and the second pulse and strength thereof change depending on the region where each reflection portion is located.
• a peak value of the pulse from the reflection portion is sometimes used as a value representing strength of the terahertz wave pulses.
• the first reflection portion 114 and the second reflection portion 115 are located within the light collecting process region (region A), and within this region, the positions of the reflection portions relatively move with the movement of the collecting position of the terahertz wave pulses.
• a time interval At in FIG. 6B does not change so much.
• the time interval At changes by about a difference of the angle component with scaling up and down of the beam diameter of the terahertz wave pulses reaching the generation/detection unit 101, which change being mere as compared to the movement of the reflection portion.
• a ratio of a peak value Ai of the first pulse from the first reflection portion 114 to a peak value A2 of the second pulse from the second reflection portion 115 changes depending on loss or dispersion due to the physical properties or the structure of the object to be measured and also due to the collecting position. This is because a
• reflection signal from around the collimated region of the optical system in the shaping unit 102 is focused on the generation/detection unit 101, while a
• reflection signal from a position away from the focus of the optical system is incident in an unfocused manner on the generation/detection unit 101. More specifically, when the photoconductive element is used as the generation/detection unit 101, the antenna pattern on the photoconductive element spatially changes detection sensitivity in the element. Space distribution of the sensitivity can be regarded as a space filter. Thus, depending on the positional relationship between the light collecting process region of the optical system and the reflection
• generation/detection unit 101 changes for the pulse signals from the reflection portions.
• a ratio of strength of the pulses from the reflection portions changes depending on the positional relationship.
• the photoconductive element is used as an example of the generation/detection unit 101, but not limited to this. Even if the detection element does not have a function of a space filter, the same operation can be performed by combining structural space filters such as minute apertures .
• the first reflection portion 114 and the second reflection portion 115 are located within the collimated region (region B) , and within this region, the positions of the reflection portions relatively move with the movement of the collecting position of the terahertz wave pulses.
• the time interval At in FIG. 6B does not change so much because the optical moving distance of each reflection portion is substantially proportional to the physical moving distance as described above.
• a strength ratio between the first pulse and the second pulse mainly depends on loss or dispersion due to the physical properties or the structure of the object to be
• reflection portion 114 and the second reflection portion 115 range the light collecting process region (region A) and the collimated region (region B) , and to satisfy this condition, the positions of the reflection portions relatively move with the movement of the collecting position of the terahertz wave pulses. This state is herein also referred to as a mixed region (region A+B) . At this time, since propagation
• the time interval At in FIG. 6B changes depending on the
• the peak value Ai of the first pulse from the first reflection portion 114 changes depending on the position of the first reflection portion 114 in the region A.
• the strength ratio of the peak value Ai of the first pulse from the first reflection portion 114 to the peak value A 2 of the second pulse from the second reflection portion 115 changes depending on the collecting position of the terahertz wave pulses.
• the depth of focus approximates to n ( ⁇ ) ⁇ /2 (NA) 2 . From this relationship, the depth of focus is estimated to be several mm for the terahertz waves.
• ⁇ is a wavelength
• ⁇ ( ⁇ ) is a refractive index (also herein referred to as
• NA is the number of apertures of the optical system.
• the optical system of the shaping unit 102 functions as the confocal optical system.
• the peak value of the first pulse can be monitored to specify the position of the first reflection portion 114.
• the depth of focus being sufficiently small for the object to be measured refers to a size such that the terahertz wave pulses cannot be recognized as a structure. Specifically, this refers to an effective size of about 1/20 ⁇ to 1/100 ⁇ of a wavelength ⁇ used, or an effective size corresponding to a half width of the terahertz wave pulses.
• the effective size includes refractive indexes of the object to be measured and an environment around the object to be measured. Typically, the size is several ⁇ to- several tens of ⁇ .
• the measurement position information obtaining unit 107 uses the first pulse and the second pulse from the object to be measured to increase measurement accuracy for the position of the first reflection portion 114.
• a collecting position Z is an amount of adjustment by the collecting position adjusting unit 106. More
• the collecting position Z refers to a relative amount of movement with respect to a geometric optical focus.
• the collecting position Z is equivalent to the relative amount of movement of the collecting position.
• FIG. 7A plots the interval At between the first pulse and the second pulse with the change of the collecting position Z. When the amount of adjustment of the collecting position Z is increased, the first
• the reflection portion 114 and the second reflection portion 115 of the object to be measured move from the collimated region (region B) to the light collecting process region (region A) .
• the amount of change of the pulse, interval At is smaller than the amount of adjustment of the collecting position Z as described above.
• the terahertz wave pulses from the reflection portions to the generation/detection unit 101 have different relative propagation lengths, and thus the pulse interval At tends to increase with respect to the amount of adjustment of the collecting position Z.
• FIG. 6A when the first reflection portion 114 is located in the light
• the amount of adjustment of the collecting position Z with a tendency of increase in the pulse interval At can be calculated to obtain a position where the collecting position ⁇ of the terahertz wave pulses matches the first reflection portion of the object to be measured. More specifically, a position is obtained where the light collecting process region, the interface of the collimated region, and the first reflection portion of the object to be measured match. In FIG.
• the collecting position Z is moved from the mixed region (region A+B) to- the light collecting process region (region A) , and the amount of adjustment of the collecting position Z with a tendency of saturation of the pulse interval At can be calculated to obtain a position where the collecting position P 2 of the terahertz wave pulses matches the second reflection portion 115 of the object to be measured. More
• a position is obtained where the light collecting process region, the interface of the collimated region, and the second reflection portion 115 of the object to be measured match.
• the change of the time interval between the first pulse and the second pulse with the movement of the collecting position of the terahertz wave pulses is used herein.
• Change information of the time interval can be used to specify the reflection portions of the object to be measured even under the condition that the light collecting process region and the collimated region of the beams of the terahertz wave pulses are mixed. This can increase measurement accuracy of the thickness t and the average refractive index n(ave) of the object to be measured.
• FIG. 7B plots the peak value Ai of the first pulse from the object to be measured with the change of the collecting position Z.
• the terahertz wave pulses propagate through the object to be measured as collimated beams, and thus a rate of change of the peak value Ai is low. This is because strength per unit area of the terahertz wave pulses focused on the generation/detection unit 101 does not change so much even if the . position of the first reflection portion 114 changes in the collimated region (region B) .
• a point of change of the gradient can be calculated to obtain a position where the collecting position ⁇ of the terahertz wave pulses matches the first reflection portion 114 of the object to be measured.
• asymptotes are
• a position where the asymptotes cross is determined as a position where the first reflection portion 114 of the object to be measured matches the collecting position Pi of the terahertz wave pulses. More specifically, a position is obtained where the light collecting process region, the interface of the collimated region, and the first reflection portion 114 of the object to be measured match.
• the peak value A 2 of the second pulse from the object to be measured with the change of the collecting position Z can be plotted to obtain a position where the collecting position P 2 of the terahertz wave pulses matches the second reflection portion 115 of the object to be measured. More
• FIG. 7C shows a variant of FIG. 7B, where, to calculate the gradient of the peak value, a differential value of the peak value Ai rather than the asymptote of the peak value is used.
• a differential value of the peak value Ai rather than the asymptote of the peak value is used.
• points of change of the differential value are calculated, and a midpoint of a connection thereof is calculated. The midpoint is determined as a
• processing can be performed for the second reflection portion 115 of the object to be- measured to obtain a position where the collecting position P 2 of the terahertz wave pulses matches the second reflection portion 115 of the object to be measured.
• he change of the time waveform herein is a change of the peak values of the first pulse and the second pulse with the movement of the collecting position of the terahertz wave pulses.
• Change information of the peak values can be used to specify the reflection portion of the object to be measured even under the condition that the light collecting process region and the collimated region of the beams of the terahertz wave pulses are mixed. This can increase measurement accuracy of the thickness t and the average refractive index n(ave) of the object to be measured.
• Such methods are selected depending on the property of the object to be measured or the configuration of the apparatus.
• FIG. 6B when the first pulse and the second pulse are close to each other, the pulses may be superimposed to change the time waveform.
• the time interval At or the peak values Ai and A 2 has an error, which may reduce processing accuracy of the measurement position information obtaining unit 107.
• FIG. 17 plots an assumed time interval At converted from the thickness of the object to be measured and a time interval At actually measured.
• terahertz wave pulses at this time is 350 femtoseconds.
• the ordinate and the abscissa in FIG. 17 should indicate the same value, but actually, when the first pulse and the second pulse are close to each other, the ordinate and the abscissa indicate different values. Specifically, if the pulses from the
• reflection portions are close to a time region of about 1.5 times (about 530 femtoseconds in FIG. 17) the half width of the terahertz wave pulses used, the assumed time interval may be deviated from the measured time interval .
• the measurement position information obtaining unit 107 desirably includes compensation processing as described below.
• the compensation processing a reference waveform of previously measured terahertz wave pulses is used to perform deconvolution of
• an impulse response waveform from the object to be measured As a reference waveform in FIG. 8B, for example, a complete reflection waveform of the terahertz wave pulses formed by metal or the like is used.
• an impulse response waveform in FIG. 8C can be obtained. Since the obtained impulse
• response waveform has a smaller half width than the first pulse and the second pulse shown in FIG. 6B, even with the first pulse and the second pulse being close to each other, processing accuracy of specification of the first reflection portion of the object to be
• a reference waveform may be used to perform peak analysis. It is assumed that a measured waveform in FIG. 9A can be
• the first pulse and the second pulse are separated from the measured waveform using the reference waveform.
• FIG. 9C it is assumed that the measured waveform can be reconstructed by a combination of two reference waveforms, and peak analysis is performed. From a result of the peak analysis in FIG. 9C, two reference waveforms with adjusted position, strength and phase on a time axis can be obtained as the first pulse and the second pulse. From the adjusted two reference
• the peak analysis by regression analysis is performed as the compensation processing, and thus processing accuracy of specification of the first reflection portion of the object to be measured can be maintained even if the first pulse and the second pulse are close to each other.
• the measurement position information obtaining unit 107 monitors the changes of the time waveforms of the first pulse and the second pulse reflected from the first reflection portion 114 and the second reflection portion 115 with the change of the collecting position of the terahertz wave pulses.
• An amount of adjustment ⁇ by the measurement position information obtaining unit 107 monitors the changes of the time waveforms of the first pulse and the second pulse reflected from the first reflection portion 114 and the second reflection portion 115 with the change of the collecting position of the terahertz wave pulses.
• the optical path length difference Di is an amount of adjustment by the delay optical unit 104 required for the
• the physical property obtaining unit 108 calculates the thickness t and the average refractive index n(ave) of the region between the first reflection portion 114 and the second reflection portion 115 of the object to be measured. More specifically, an amount of adjustment Z 2 by the collecting position adjusting unit 106 when the collimated region of the terahertz wave pulses matches the second reflection portion 115 and an optical path length difference D 2 by the delay optical unit 104 required for detecting the second pulse are obtained.
• the thickness t and the average refractive index n(ave) of the region between the first reflection portion 114 and the second reflection portion 115 are calculated.
• a calculation method of the thickness t and the average refractive index n(ave) of the region between the first reflection portion 114 and the second reflection portion 115 is as follows. As the detailed deriving method described in PTL 2, when the object to be measured relatively moves substantially in the
• the propagation direction of the terahertz wave pulses, the thickness t and the average refractive index n(ave) are calculated by Expressions (1) and (2) below.
• the expressions are obtained by writing expressions using an incident angle, an incident position, an angle of refraction, or the like of the pulses with respect to the object to be measured and straightening the
• Expression (1) includes a term of
• I D2 - D1 I nxt-
• n 2 jsin 2 ⁇ + Jsin 4 ⁇ + 4(1 - sin 2 ⁇ ) x (l + ⁇ — j * ⁇ ⁇ ( 2 )
• Sin ⁇ is the number of apertures (NA) in the atmosphere of the optical system in the shaping unit 102.
• the physical property obtaining unit 108 calculates the refractive index from a ratio of the change of the collecting position to the change of the optical path length difference when the collecting position of the terahertz wave pulses is changed from the measurement references. Then, the thickness is calculated.
• n ( ⁇ ) ⁇ /2 (NA) 2 n ( ⁇ ) ⁇ /2 (NA) 2 , and thus an increase in the number of apertures reduces the size of the collimated region.
• ⁇ approximates to A/nw 0 (rad) .
• wo is a beam spot radius of the terahertz wave pulses. The beam spot radius of the terahertz wave pulses is reduced with increasing number of apertures.
• the number of apertures is desirably determined so as to set the beam spot radius to a value not exceeding a desired measurement range.
• the increase in the number of apertures reduces the size of the collimated region, and thus the pulse interval, as shown in in FIG. 7A, steeply changes for the amount of adjustment by the collecting position adjusting unit 106. This tends to cause a steep change of the pulse interval for a minimum adjustment ability of the collecting position adjusting unit 106.
• the collecting position adjusting unit 106 does not have a sufficient minimum adjustment ability for the change of the pulse interval, detection accuracy of the reflection portion of the object to be measured is reduced.
• the size of the collimated region may be increased, and the amount of change of the pulse interval for a minimum amount of adjustment by the collecting position adjusting unit 106 may be reduced to observe the change of the pulse interval in detail.
• the change of the pulse interval may exceed an adjustment limit of the collecting position adjusting unit 106.
• the size of the collimated region is set so that the change of the pulse interval falls within the adjustment limit by the collecting position adjusting unit 106.
• the detection accuracy of the reflection portion has an influence on processing accuracy of the above described physical property obtaining unit 108.
• the increase in the size of the collimated region tends to increase processing accuracy of the physical property obtaining unit 108.
• the number of apertures is desirably determined depending on measurement accuracy of the required thickness t and average refractive index n(ave) of the object to be measured.
• the number of apertures is desirably determined so as to satisfy demands of a required measurement range set by a beam spot radius and the processing accuracy of the physical property obtaining unit 108.
• At least a region of about an interval between the first reflection portion 114 and the second reflection portion 115 is desirably ensured as a depth of focus. This is because if the depth of focus is extremely smaller than the interval between the first reflection portion 114 and the second reflection portion 115, a change of the optical path length by an influence of the light collecting process region is superimposed on the time interval between the pulses from the
• the obtained tomographic image needs to be further subjected to processing for reducing the influence of the optical system.
• the number of apertures of the optical system is desirably selected so as to further satisfy a condition of the collimated region considering a required horizontal observation region and the interval between the first reflection portion 114 and the second reflection portion 115.
• FIG. 4 is a typical operation flow of the apparatus of this embodiment.
• the apparatus uses the delay optical unit 104 to adjust the optical path length difference to a position where the first pulse from the first reflection portion of the object to be measured can be detected (S101) .
• the optical path length difference may be a machine origin determined by the delay optical unit 104, or may be determined by measuring a placement state of the object to be measured using a camera or a distance measuring unit.
• a time waveform of the terahertz wave pulses may be measured once to determine the optical path length difference.
• he waveform obtaining unit 105 obtains the time
• the waveform of the terahertz wave pulses by time-domain spectroscopy, and stores information of the time waveform and the collecting position of the terahertz wave pulses in a storage unit of the apparatus (S102).
• the stored collecting position is equal to an amount of adjustment by the collecting position adjusting unit 106.
• the time waveform of the terahertz wave pulses includes at least the first pulse and the second pulse. It is determined whether the collecting position is to be moved. This determination is made, for example, by determining whether a fixed number of times of
• the determination is made by determining whether a previously determined amount of movement of the collecting position is ensured.
• the determination is desirably made by determining whether the collecting position of the terahertz wave pulses is moved from the first
• the collecting position adjusting unit 106 is used to slightly move the collecting position of the terahertz wave pulses (S103) . Then, the time waveform of the terahertz wave pulses is again obtained by the waveform obtaining unit 105, and the information of the time waveform and the collecting position of the terahertz wave pulses (the amount of adjustment by the collecting position
• the apparatus uses the measurement position information obtaining unit 107 to calculate the first reflection portion 114 of the object to be measured (S104) . Specifically, from the change of the time waveform of the terahertz wave pulses for the amount of adjustment by the collecting position adjusting unit 106 as shown in FIGS. 7A, 7B and 7C, a position is specified where the first reflection portion 114 matches the collecting position Pi of the terahertz wave pulses.
• the apparatus uses the collecting position adjusting unit 106 to move the collecting position of the terahertz wave pulses to the first reflection portion 114 (S105) .
• the storage unit has already obtained the time waveform of the terahertz wave pulses for the desired amount of adjustment by the collecting position adjusting unit 106
• the amount of adjustment by the collecting position adjusting unit 106 required for the movement to the first reflection portion 114 may be invoked.
• the physical property obtaining unit 108 obtains the first pulse from the first reflection portion 114 (S106) .
• the first pulse is obtained from a time waveform of the terahertz wave pulses measured by the waveform obtaining unit 105.
• the time waveform stored in the storage unit may be used to invoke the time waveform of the terahertz wave pulses
• obtaining unit 108 obtains the optical path length difference Di and the collecting position Zi
• the collecting position adjusting unit 106 moves the collecting position P 2 of the terahertz wave pulses to a position matching the second, reflection portion 115 of the object to be measured (S107) .
• the measurement position information obtaining unit 107 calculates the position of the second reflection portion 115 of the object to be measured by invoking information of the time waveform of the terahertz wave pulses for the amount of adjustment by the collecting position adjusting unit 106 stored in the storage unit.
• the collecting position adjusting unit 106 may
• the measurement position information obtaining unit 107 may monitor the position of the second reflection portion 115 in real time. Similar to S105, when the storage unit has already obtained the time waveform of the terahertz wave pulses for the desired amount of adjustment by the collecting position adjusting unit 106, the amount of adjustment by the collecting position adjusting unit 106 required for movement to the second reflection portion 115 may be invoked.
• the physical property obtaining unit 108 obtains the second pulse from the second reflection portion 115 (S108) .
• the second pulse is obtained from the time waveform of the terahertz wave pulses measured by the waveform obtaining unit 105.
• the time waveform stored in the storage unit may be used to invoke the time waveform of the terahertz wave pulses
• obtaining unit 108 obtains the optical path length difference D 2 and the collecting position Z 2
• the physical property obtaining unit 108 uses any one of Expressions (1) to (4) to calculate the thickness t and the average refractive index n(ave) of the region between the first reflection portion 114 and the second reflection portion 115 from the amount of change
• the physical property measurement apparatus of this embodiment obtains the thickness t and the average refractive index n(ave) of the object to be measured. According to the apparatus
• the position of the reflection portion of the object to be measured is calculated by the changes of the time waveforms of the first pulse and the second pulse with the change of the collecting position of the terahertz wave pulses.
• the position of each reflection portion can be accurately specified.
• This ca provide an apparatus that can increase detection accuracy of the thickness t and the average refractive index n(ave) of the region between the first reflection portion and the second reflection portion.
• the apparatus and method of this embodiment use the terahertz wave pulses.
• using transmission of the terahertz wave pulses allows specification of the physical properties of the inner structure at a depth of about several hundreds of ym to several tens of mm.
• Embodiment 1 Another aspect for carrying out the idea of the present invention will be described with reference to the drawings.
• This embodiment is a variant of Embodiment 1, Specifically, this embodiment relates to an apparatus and a method configured to identify an object to be measured from a shape of terahertz wave pulses.
• FIG. 2 is a schematic configuration diagram of a
• This apparatus includes a portion
• the portion configured to identify the object to be measured includes at least: a database 211 that stores physical property information and a time waveform of terahertz wave pulses for each material; a waveform adjusting unit 209 configured to select, from the database 211, a candidate material for a region between a first reflection portion 114 and a second reflection portion 115 by an average refractive index n(ave) obtained by the apparatus, and adjust a time waveform of the candidate material to a time waveform including an influence of a thickness t and the stored physical property; a waveform comparing unit 210 configured to compare the measured time waveform of the terahertz wave pulses with the time waveform by the waveform adjusting unit 209; and a physical property specifying unit 212 configured to specify a material highly correlated with the measured waveform from an output from the waveform comparing unit 210.
• database 211 is frequency spectrum information of a terahertz wave region.
• the stored time waveform of the terahertz wave pulses is desirably the time waveform measured by the apparatus described in this embodiment.
• time waveforms measured by the same apparatus do not always need to be used.
• time waveforms measured by the same apparatus configuration may be used.
• Time waveforms measured by other apparatus configurations may be used if an influence typical of the apparatus (accuracy or measurement band) is already known.
• a difference between the apparatuses is stored in the database 211 as a system function.
• a measurement condition (temperature, humidity, or atmosphere) when each material is measured is desirably stored in the database 211 as a system function.
• measurement is also stored in the database 211.
• the time waveform stored in the database 211 desirably includes a first pulse and a second pulse.
• the average refractive index n(ave) of the object to be measured that is measured by the physical property obtaining unit 108 configured to adjust the time waveform of the material stored in the database 211 is referred to, and a material having a similar average refractive index n(ave) is screened from the database 211.
• the waveform adjusting unit 209 adjusts a time waveform of a candidate material obtained by screening.
• the average refractive index n(ave) and the thickness t of the object to be measured that are measured by the physical property obtaining unit 108 is referred to, and when the outer shape (thickness) is different from that of the material stored in the database 211, an interval between the first pulse and the second pulse of the time waveform invoked from the database 211 is adjusted.
• physical property information for example, refractive index dispersion ⁇ ( ⁇ ), an absorption coefficient, a frequency spectrum, or the like
• the influence of dispersion typical of the material is compensated to adjust the shape of the time waveform of each pulse.
• the system function of the candidate material stored in the database 211 may be referred to, and convolution of the adjusted time waveform may be performed.
• the waveform comparing unit 210 compares the time waveform of the candidate material adjusted by the waveform adjusting unit 209 with the waveform measured by the waveform obtaining unit 105. Specifically, residuals of the time waveform by the waveform
• waveform obtaining unit 105 are output.
• the waveform obtaining unit 105 is checked.
• An area of comparison in the time waveform may be the entire time waveform obtained, or only a characteristic portion (for example, the first pulse or the second pulse) .
• the physical property specifying unit 212 refers to the output from the waveform comparing unit 210 to select a candidate material closest to the object to be measured. Physical properties (for example, refractive index dispersion ⁇ ( ⁇ ), an absorption coefficient, a frequency spectrum, or the like) and a type of the object to be measured are presented to the operator of the apparatus.
• FIG. 5 is a typical operation flow relating to the
• the apparatus moves the collecting position of the terahertz wave pulses to a spot where a physical property is to be specified.
• the apparatus calculates the average refractive index n(ave) and the thickness t of the object to be measured by the steps S101 to S109 described in Embodiment 1 (S201) .
• Such information is output from the physical property obtaining unit 108.
• the time waveform of the terahertz wave pulses relating to the object to be measured is output.
• a plurality of candidate materials of the object to be measured is selected from the materials stored in the database 211 by referring to the average refractive index n(ave) output from the physical property obtaining unit 108.
• the waveform adjusting unit 209 adjusts the time waveform linked to each candidate material (S202).
• the waveform comparing unit 210 compares the time waveform of the terahertz wave pulses output from the waveform adjusting unit 209 with the time waveform of the terahertz wave pulses output from the waveform obtaining unit 105 (S203).
• the physical property specifying unit 212 refers to the output from the waveform comparing unit 210 to specify a candidate material closest to the object to be
• the physical property specifying unit 212 then presents the physical property and the type of the object to be measured to the operator. For example, refractive index dispersion ⁇ ( ⁇ ), an absorption coefficient, a frequency spectrum, or the like are presented as the physical properties.
• Step S202 a plurality of candidate materials is selected to collectively adjust time waveforms, an action of selecting one material and then performing the steps S202 to S204 may otherwise be performed several times.
• the physical property specifying unit 212 desirably determines a condition for the object to be measured to match the candidate material. In the method of collectively selecting the candidate
• the method of successively selecting the candidate materials and checking matching reduces a load required for calculation for each processing, thereby reducing the need for large-scale calculation. Thus, power saving and a cost reduction of the apparatus can be expected .
• the time waveform of the terahertz wave pulses from the reflection portion of the object to be measured is compared with the time waveform of the material previously stored in the database to check the physical property of the object to be measured.
• This can provide an apparatus that allows specification of the material for the object to be measured. According to the measurement method of this embodiment, the material for the object to be measured can be specified for the same reason.
• This embodiment is a variant of the above described embodiment. Specifically, this embodiment has a different configuration of a portion configured to generate and detect terahertz wave pulses.
• FIGS. 3A and 3B are schematic configuration diagrams of a physical property measurement apparatus of this embodiment.
• a variant of the measurement apparatus of Embodiment 1 is shown.
• a difference from Embodiment 1 is that two elements: a generation unit 313 and a detection unit 314, is used in place of the
• generation/detection unit 101 the same photoconductive element is used for generation and detection, but this element is divided into two parts to increase flexibility in selection.
• an element having a high output of terahertz wave pulses can be selected as the generation unit 313, and an element having high
• detection sensitivity can be used as the detection unit 314.
• increasing selectivity of the apparatus can easily address various demands for the apparatus.
• a shaping unit 102 in FIG. 3A uses four mirrors 316 to collect terahertz wave pulses on an object to be measured, and at this time, an application direction of excitation lights Li and L 2 matches an application direction of the terahertz wave pulses.
• the shaping unit 102 when the shaping unit 102 includes the generation unit 313 and the detection unit 314, the shaping unit 102 can be moved in the application direction of the excitation lights to move a collecting position of the terahertz wave pulses. This movement is performed by an actuator 315 provided in the shaping unit 102.
• the actuator can move two mirrors 318 on the side of the object to be
• the collecting position of the terahertz wave pulses may be moved by an actuator (not shown) provided on the side of the object, to be measured.
• an incident angle of the terahertz wave pulses incident on the object to be measured can be variable.
• adjustable incident angle allows adjustment of a measurement region such that, for example, with an angle with respect to a vertical line (line
• the incident angle is increased to obtain information on a surface of the object to be measured surface, and the incident angle is reduced to obtain information on a deep region of the object to be measured.
• the measurement region of the object to be measured can be limited to reduce reflected signals from unnecessary spots, and thus an increase in
• FIG. 3A is a variant of Embodiment 1, but may also be applied to Embodiment 2.
• a time axis of a time waveform of terahertz wave pulses can be converted into a distance.
• the time waveform of the terahertz wave pulses described above can be captured as an A-scan image of a tomographic image.
• an optical axis along which the terahertz wave pulses propagate can be moved to cross a direction of the terahertz wave pulses incident on the object to be measured to obtain a B-scan image or a three- dimensional tomographic image.
• FIG. 13 is a schematic configuration diagram of a
• the measurement apparatus of Embodiment 1 is applied to the tomographic image obtaining apparatus.
• the measurement apparatus of Embodiment 2 or 3 can be similarly applied to the tomographic image obtaining apparatus.
• This apparatus includes, in addition to the apparatus configuration of Embodiment 1: a moving stage 1301 configured to
• an image constructing unit 1302 configured to relate a position (observation point) of the moving stage 1301 to a time waveform output from a waveform obtaining unit 105 to construct a tomographic image of the object to be measured; a characteristic region extracting unit 1303 configured to extract a characteristic region from the tomographic image; and a correcting unit 1304 configured to
• the moving stage 1301 moves the object to be measured so as to cross an application direction of the terahertz wave pulses.
• the position of the moving stage 1301 is not limited to this, such that otherwise the moving stage 1301 may be placed in a position for moving the optical axis of the terahertz wave pulses.
• the moving stage 1301 may be placed in a position for moving the optical axis of the terahertz wave pulses.
• the moving stage 1301 may be a unit that can relatively move the object to be measured and the terahertz wave pulses so as to cross each other.
• the moving stage 1301 may also have a function of moving the collecting position of the
• terahertz wave pulses in the application direction of the terahertz wave pulses.
• the image constructing unit 1302 relates information of the measured waveform by the waveform obtaining unit 105 to the position (also referred to as the observation point in this
• the moving stage 1301 to construct a desired tomographic image.
• the moving stage 1301 is moved in one direction to form a B-scan tomographic image.
• the moving stage 1301 is two-dimensionally moved to construct a three-dimensional tomographic image.
• the moving stage 1301 is two-dimensionally moved with the optical path length difference by the delay optical unit 104 being fixed to construct a C- scan tomographic image.
• the characteristic region extracting unit 1303 extracts a characteristic region from the tomographic image constructed by the image constructing unit 1302. An operator refers to- the tomographic image and selects a region of note as the characteristic region.
• the apparatus may refer to the B-scan or C-scan tomographic image to automatically detect and extract a position where an interface of the reflection portion is discontinuous. At this time, the apparatus may refer to the B-scan or C-scan tomographic image to automatically detect and extract a position where an interface of the reflection portion is discontinuous. At this time, the
• the correcting unit 1304 uses the physical property obtaining unit 108 to calculate the average refractive index n(ave) and the thickness t for the selected characteristic region, and refers to the information to correct an obtained image. Specifically, the correcting unit 1304 adjusts a
• the material of the characteristic region and the physical property of the material may be specified and displayed in a color- coded manner according to the specified information.
• FIG. 14 is a typical operation flow relating to the apparatus of this embodiment.
• FIG. 15A is a schematic diagram of skin used as an
• epidermis As a typical structure of skin, epidermis has a thickness of several hundreds of ⁇ and dermis has a thickness of several mm.
• the epidermis contains epidermal cells, pigment cells, and Langerhans cells, and it has keratin of a thickness of several tens of ⁇ on an outermost surface.
• the dermis
• the elastin contains collagen and elastin.
• the collagen contains collagen and elastin.
• the elastin contains collagen and elastin.
• embodiments images an outermost surface of the epidermis, a boundary between the epidermis and the dermis, and a boundary between the dermis and subcutaneous tissue.
• FIG. 15B is a schematic diagram when skin has cancer tissue. It is known that cancer tissue has higher moisture content than healthy tissue. Thus, a difference in moisture content can be imaged to identify cancer tissue.
• a living body typified by skin is used as an object to be measured, it is difficult to obtain a tomographic image relating to a region at a depth of several mm to several tens of mm with accuracy of several tens of ⁇ to several hundreds of ⁇ because of high absorption or scattering of visible lights or infrared rays on the living body.
• Such a tomographic image can be obtained by an ⁇ apparatus configuration that uses transmission of terahertz waves and increases measurement resolution with the terahertz waves in the form of pulses.
• FIG. 16A is a schematic diagram of an object to be measured and a tomographic image thereof. A B-scan tomographic image is shown in FIG. 16A.
• a difference in physical property between areas that constitute the object to be measured causes a difference in propagation speed of the terahertz wave pulses, and thus causes a different optical length between the areas.
• a position of an interface partially changes as compared to a section of the object to be measured .
• characteristic region extracting unit 1303 selects a characteristic region (S302). For example, in FIG. 16A, a region between an outermost surface of epidermis and an interface between the epidermis and dermis as a characteristic region is a first characteristic point 1601. A region between an outermost surface of cancer tissue and an interface between the cancer tissue and the dermis is a second characteristic point 1602. A region between the interface between the epidermis and the dermis and an interface between the dermis and subcutaneous tissue is a third characteristic point 1603.
• the apparatus uses the moving stage 1301 in FIG. 13 and the actuator 116 to move an observation region of terahertz wave pulses to a characteristic region to be noted (S303) .
• the steps S101 to S109 are used to calculate an average refractive index n(ave) and a thickness t of each observation point (S304).
• Physical properties of each characteristic region are obtained using the steps S202 to S204 (S305) . Specifically, the physical properties are obtained to specify a material for the
• the correcting unit 1304 refers to the average refractive index n(ave) and the
• characteristic regions are presented with different display manners depending on the materials. For example,
• the materials are presented in different colors .
• the material for the object to be measured is specified by the obtained information of the tomographic image.
• This can provide a tomography apparatus that can collect a change of the image by the physical property of the material, and specify a material for the corrected portion.
• a tomographic image obtaining method according to this embodiment can collect a change of the image by the physical property of the material, and specify a material for the corrected portion.
• electromagnetic waves having any wavelengths can be used in measuring an object to be measured having substantially the same size as the collimated region of the confocal optical system.
• wavelength of 1 m to 100 ⁇ (frequency band of a 300 MHz to 3 THz)
• centimeter waves having a wavelength of 10 mm to 100 mm (frequency band of 3 GHz to 30 GHz) may be used.
• photoconductive elements are used as the generation unit 313 and the detection unit 314.
• a dipole antenna having a length of 20 m and a width of 10 ⁇ is patterned on each semiconductor film.
• the shaping unit 102 includes four parabolic mirrors.
• the object to be measured is placed on the actuator 116, and a collecting position of the terahertz wave pulses is adjusted by the actuator 116.
• the collecting position adjusting unit 106 is a driver configured to control the actuator 116.
• the light source 103 uses a femtosecond fiber laser having a central wavelength of 1.56 ⁇ , a pulse width of 30 femtoseconds, and a repetition frequency of 50 MHz.
• a wavelength conversion element PPLN
• PPLN wavelength conversion element
• the delay optical unit 104 includes a direct-acting stage and a retroreflector . Position information of the direct-acting stage is input to the waveform obtaining unit 105.
• the waveform obtaining unit 105 includes a current amplifier and an A/D board. An output from the current amplifier corresponding to position information of the delay optical unit 104 is . successively plotted to construct a time waveform of the terahertz wave pulses.
• the measurement position information obtaining unit 107 and the physical property obtaining unit 108 include a processor.
• FIG. 10A A configuration of the object to be measured used in this example is shown in FIG. 10A.
• two objects to be measured are used.
• a stack of polyethylene and quartz via an air space is used as an object to be measured 1.
• a stack of polyethylene, vinyl chloride, and quartz is used as an object to be measured 2.
• An overall thickness of the object to be measured 1 is about 1.1 mm.
• An overall thickness of the object to be measured 2 is about 0.9 mm.
• FIGS. 10B and IOC show time waveforms of the terahertz wave pulses from the objects to be measured obtained by the waveform obtaining unit 105. From the time waveforms, reflection pulses from four interfaces can be checked in the object to be measured 1 (FIG. 10B) , and reflection pulses from five interfaces can be checked in the object to be measured 2 (FIG. IOC) .
• the first interface is the first interface
• reflection portion 114 and the last interface is the second reflection portion 115.
• FIGS. 11A and 11B show an operation of the measurement position information obtaining unit 107.
• FIG. 11A relates to the object to be measured 1, and a change of a pulse interval for the collecting position similar to that in FIG. 7A can be checked. From FIG. 11A, an amount of adjustment of the collecting position Z where a pulse interval At tends to increase is determined as a position of the first reflection portion 114.
• FIG. 11B relates to the object to be measured 2, and a tendency similar to that of the object to be measured 1 can be checked.
• FIGS. 12A and 12B also show the operation of the
• FIG. 12A an amount of adjustment of the collecting position Z where a gradient of a peak value changes is calculated from an asymptote for each object to be measured, and this is a position of the first reflection portion.
• FIG. 12B a change of a
• differential value of a peak value for the collecting position is similar to that in FIG. 7C. From FIG. 12B, an amount of adjustment of the collecting position Z where the gradient of the peak value changes is calculated from the point of change of the differential value for each object to be measured, and this is determined as a position of the first reflection portion 114. A position of the second reflection portion 115 is also calculated from the change of the peak value of the second pulse in the same manner.
• the physical property obtaining unit 108 may only be required to ensure a relative relationship between the amount of movement
• the measurement position information obtaining unit 107 detects the reflection portion by the change of the pulse interval. Results of output from the measurement position information obtaining unit 107 and the physical property obtaining unit 108 at this time are shown in the table below.
• the collecting position is adjusted by moving the object to be measured.
• calculation by the physical property obtaining unit 108 uses Expressions (1) and (2) .
• sin ⁇ as the number of apertures is 0.24.
• an incident angle of the terahertz wave pulses with respect to the object to be measured is about 15°.
• correction with the incident angle is performed. It is apparent from the calculation result of the physical property obtaining unit 108 that the thickness is close to the previously measured thickness of each object to be measured.

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• 2012
  • 2012-03-04 JP JP2012047462A patent/JP2013181929A/ja active Pending
• 2013
  • 2013-02-27 WO PCT/JP2013/056060 patent/WO2013133294A1/fr not_active Ceased
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